I paid two-thirds of my son’s down payment in 2013 — should I ask for a percentage of his condo’s appreciation in value?

After several conversations, my son finally agreed to put up one-third of the 20% down payment for a newly renovated condo and I paid the other two-thirds of the down payment.

My son continued to pay for mortgage (both interest and principle) so his accumulation of principle paid should be considered as further investment on top of down payment. For example, if my son paid down additional $20,000 in principle, then the investment amount should be down payment, plus $20,000 so his share of profit should be larger than one-third.

“Four hostile newspapers are more to be feared than a thousand bayonets...” ― Napoléon Bonaparte