It is a treatment for PGD applied by a therapist composed of 8-10 treatment sessions. Each session lasts approximately 60 minutes. No weekly support call will be provided.

The sessions will take place by videoconference. Main components of the treatment: Motivation for change, Psychoeducation, Behavioral activation, Exposure, Mindfulness and compassion strategies, integration of loss, restoration and reconstruction of meaning, Cognitive reappraisal and Relapse prevention.

It is a self-applied instrument to assess the frequency and severity of depression. It also measures the level of avoidance, work, academic, and home interference, and social interference associated with depression. Psychometric properties; Cronbach's alpha of 0.91 to 0.94 in the original version and good convergent and discriminant validity.

Cronbach's alpha of 0.93 in the Spanish adaptation and excellent convergent and discriminant validity. It consists of 5 items that are scored on a scale of 0 to 4. It is calculated by adding the score of the 5 items and the maximum score is 20.

It is a self-applied instrument to assess two independent dimensions of affectivity: Positive Affect (PA) and Negative Affect (NA). Psychometric properties; excellent internal consistency in the original version (α = 0.84 to 0.90) and convergent and discriminant validity. Excellent internal consistency in the Spanish adaptation (α =0.87 to 0.91). It consists of 20 items that are scored on a 1-5 scale. It has two subscales: positive affect (10 items) and negative affect (10 items). It is calculated by adding each of the items on the two scales separately. The maximum score is 50 for each of the subscales.

It is a self-applied instrument to assess health-rated quality of life. Psychometric properties; high test-retest reliability (r = .87) and internal consistency (α = .92) in the original version and good test-retest reliability and internal consistency (α = 0.87) in the Spanish language adaptation. It consists of 10 items that assess a global perception of quality of life and aspects ranging from physical well-being to spiritual fulfillment. A 10-point Likert scale is used to measure satisfaction in each area.

It is a self-applied instrument to assess psychosocial functional impairment. Psychometric properties; good to excellent test-retest reliability, sensitivity to change and internal consistency (α = 0.70 to 0.94) in the original version. Good concurrent validity and excellent internal consistency in the Spanish version. It consists of 5 items that are scored on a scale of 0 (not at all) to 8 (very severely). It is calculated adding the score of all the items and the maximum total score is 40. Higher scores indicate greater interference in different areas.

It is a self-applied instrument to assess post-trauma growth and self-improvement. Psychometric properties; excellent internal consistency (α = 0.90) and acceptable test-retest reliability (around 0.71) in the original version and excellent internal consistency (α = 0.92) in the Spanish version. Is a 21-item scale built on the five-factor model (Factors: Relating to Others, New Possibilities, Personal Strength, Spiritual Enhancement, Appreciation). A 6-point likert scale is used for each item. A summation of the scores indicates the level of post-traumatic growth. Higher score indicates greater positive transformation.

It is a short form of the 39-item FFMQ (Baer et al., 2006), self-applied instrument to assess the ability to be aware in the experience of the moment.

It is a 15-item scale with a Likert response format ranging from 1 (never or very rarely true) to 5 (very often or always true). It evaluates five facets of mindfulness (Observing, Describing, Acting with awareness, Non judging internal experience, Non reactivity to internal experience). Higher scores represent higher dispositional mindfulness.

Psychometric properties; Good internal consistency is shown on all 5 scales.

It is a self-applied instrument to assess the capacity for self-compassion. Psychometric properties; good internal consistency (α = 0.86) and high correlation with the long version of the SCS (r = 0.97) in the original validation and good internal consistency (α = 0.85) and high test-retest reliability in the Spanish version.

To calculate the total self-compassion score, a total mean is calculated considering the inverse items. Subscale scores are computed by calculating the mean of subscale item responses.

It is a self-applied instrument to assess maladaptive thinking common in people with complicated grief. Psychometric properties; good internal consistency for the general scale (α = 0.83) and good test-retest reliability.

Ii is a 25-item scale which measures the degree of agreement regarding different statements with a Likert response format ranging from 0 (not at all) to 4 (very strongly). Five-factor structure (protesting the death, negative thoughts about the world, needing the person, less grief is wrong and grieving too much). The maximum score is 100. The scores of the subscale are obtained from the sum of the elements of each factor.

It is a short form of the 20-items Purpose-In-Life Test (Crumbaugh, 1968). Is a self-applied instrument to assess the personal experience of meaning of life (satisfaction and meaning of life and vital goals and purposes).

Psychometric properties; good internal consistency (α = 0.86). The total score is obtained by adding the values of the selected answer options and the maximum score is 70. Two- factor structure (satisfaction and meaning of life; vital goals and purposes).

Indicate the level of distress-interference in functioning. 1 item (from 0/"Absent" to 8/"Very severely disturbing/ disabling") assessed by the therapist.

It is an interview with 31 items that evaluates symptoms of prolonged grief in people who have lost a loved one six or more months ago the interview.

Psychometric properties; acceptable internal consistency (α = 0.86) excellent inter-rater reliability and good test-retest reliability.

Each item is answered on a 3-point likert scale (Not present, insecure or misleading and present). It is calculated by adding the scores of each item and the highest score is 93.

It is a self-applied instrument Adapted from Borkovec & Nau (1972) to assess participants' expectations (before the intervention) and satisfaction with the treatment (after the intervention).

Evaluates the logic of the intervention, satisfaction with the intervention, recommendation of the intervention to others, utility of the intervention for other psychological problems, utility of the intervention for that condition and aversion generated by the intervention. Items are scored on 0-10 scales (0 ="not at all"; 10 = "a lot"). Higher score indicates greater expectation towards treatment and satisfaction with the intervention.

• Perceived clinical utility of each part of the treatment (0 = no useful at all; 10 = maximum utility)
• Utility images, video, audio and written content (0 = no useful at all; 10 = maximum utility)
• Utility, satisfaction and help in the adherence of the weekly call (only in internet-based condition group)

It is a 7-item scale developed specifically for this study, which evaluates the preferences of the participants on the two treatment conditions (face-to-face and internet-based intervention).

The 7 items measure general preference, utility, logic and aversiveness of the treatment and recommendation of the intervention to others. The answer to each item is dichotomous: A) self-applied via the Internet (with a short weekly phone call from a therapist); B) Applied weekly face-to-face sessions of approximately 60 minutes, and carried out by a therapist.

It is a 11-item questionnaire to assess the usability and acceptance of the technology by the patient.