Alan Thicke's Widow: We Got Serious About Getting Pregnant

Alan Thicke's widow says she was far from an opportunist out for Alan's riches, and says she loved him so deeply ... they were about to expand their family when he died.

Tanya Callau tells TMZ she and Alan were finally ready to take the next step in their 11-year marriage ... by getting pregnant in 2017. She says they'd frozen her eggs 3 years ago, and planned to put them to use once Alan's youngest, 19-year-old Carter, moved out.

She says they already had an architect visit their Santa Barbara ranch in early December to draw up plans for a nursery. Alan died suddenly of a massive heart attack on December 13.

Tanya's now facing a possible lawsuit from Brennan and Robin Thicke -- who claim their stepmother is greedy and overreaching for more of their dad's estate than what's laid out in his will. She's calling BS on that, and adds ... she never threatened to go to tabloids as the boys allege.