Donnie Wahlberg and Tom Selleck have formed a close bond while working together on the CBS police drama "Blue Bloods." Wahlberg considers Selleck a father figure and the two actors have even adopted the terms "Dad" and "Son" to refer to each other off-camera. Wahlberg's generous act of leaving a large tip for an IHOP server inspired Selleck to do the same at a New York City restaurant. Wahlberg recently wished Selleck a happy birthday and expressed his gratitude for having him in his life.